Broken or damaged service neutral lines are known to cause possible damage to appliances and electronics plugged into the electrical outlet of a house or business. When a service neutral connection is broken, the voltage between the high voltage line, herein referred to as the active line, and the neutral/ground connection can be erratic. It can be lower or higher than the standard RMS value of 120 volts. This often manifests itself as a dimming and brightening of lights as the voltage lowers and raises arbitrarily. Other effects can also be seen, such as compressors in refrigerators or air conditioning units running at lower or higher speeds than normal. At high voltages, excessive current may flow through electronics that are plugged into wall outlets and destroy them. Damage can occur to smaller electronics such as nightlights, computers and computer accessories or to large appliances such as refrigerators, garage door openers and air conditioners. In some cases, fires can start from burning equipment or improperly grounded equipment can become charged to a high voltage possibly lethal to humans. Often, utility companies will pay for damaged equipment if the break in the line is before it enters the power meter but if the break occurs beyond the meter, the owner typically must pay an electrician to repair the damage and cover the cost of any damaged items. This can be costly and time consuming, both for the utility company and for the customer.
Previous attempts to solve this problem include US Patent Application Publication No. 2010/0102826 by Edwards which involves measuring the input and output current and calculating the ratio to determine if a fault exists. This is an effective method, but is somewhat costly if used for detecting broken service neutral lines and is used only at the meter at the input of a home or business. The neutral line may break inside a house due to accidental damage and may only break on a single circuit to a certain part of the house, so it is desirable to have protection both for the input to the home or business and at other locations on different circuits throughout the home or business where a broken neutral line could cause a current flow between the active line and earth ground. Also, electronic equipment used away from a home or business, such as at a hotel or conference center, needs to have its own protection, even if the building that the owner of the equipment is in does not have its own protection. This protection could be either a module that the device plugs into or integrated into the device itself.
Overvoltage protection and detection exists, but typically requires an active power supply rail to power the active components processing the input voltages to determine an overvoltage. In the case of a broken service neutral line, power supply rails themselves can be damaged or destroyed, preventing existing overvoltage detection/protection and leading to damage of electronics. A device is needed which can be plugged into an electrical outlet with an unknown voltage between the active line and neutral/earth ground line in the event that the service neutral line is broken or damaged. A device that protects against this failure must be able to determine whether the input voltage is accurate by using internal electronics that are resilient to possible changes in the input voltage and capable of outputting a signal to warn of the condition and/or cut off the current at the active line. This way, if the voltage between the active line and neutral/earth ground connection becomes too high, the device itself can function at this high voltage and still perform the process necessary to warn of the condition or prevent damage to other devices, since a regulated input voltage is not guaranteed if the service neutral line is broken or if something else such as a malfunctioning transformer affects the voltage between the active line and neutral/earth connection. The device described in this application is low-cost, prevents damage caused by overvoltage conditions in the event of a broken service neutral line, is resilient to overvoltage itself, and is installable at several points in the power grid, from the input to a house or business to the input circuitry of electronic appliances. Consequently, this device can also protect against generic overvoltage conditions as well as provide protection against broken service neutral lines.